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Observation of ferromagnetism above 900 K in Cr-GaN and Cr-AlN

H. X. Liu·Stephen Y. Wu·R. K. Singh·Lin Gu·David J. Smith·N. R. Dilley·L. Montes·M. B. Simmonds·N. Newman
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Abstract

We report the observation of ferromagnetism at over 900K in Cr-GaN and Cr-AlN thin films. The saturation magnetization moments in our best films of Cr-GaN and Cr-AlN at low temperatures are 0.42 and 0.6 u_B/Cr atom, respectively, indicating that 14% and 20%, of the Cr atoms, respectively, are magnetically active. While Cr-AlN is highly resistive, Cr-GaN exhibits thermally activated conduction that follows the exponential law expected for variable range hopping between localized states. Hall measurements on a Cr-GaN sample indicate a mobility of 0.06 cm^2/V.s, which falls in the range characteristic of hopping conduction, and a free carrier density (1.4E20/cm^3), which is similar in magnitude to the measured magnetically-active Cr concentration (4.9E19/cm^3). A large negative magnetoresistance is attributed to scattering from loose spins associated with non-ferromagnetic impurities. The results indicate that ferromagnetism in Cr-GaN and Cr-AlN can be attributed to the double exchange mechanism as a result of hopping between near-midgap substitutional Cr impurity bands.

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H. X. Liu, Stephen Y. Wu, R. K. Singh, Lin Gu, David J. Smith, N. R. Dilley, L. Montes, M. B. Simmonds, N. Newman. 2004-09-22. Observation of ferromagnetism above 900 K in Cr-GaN and Cr-AlN. https://doi.org/10.1063/1.1812581

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